Entamoeba histolytica is believed to infect a half billion people annually. Approximately 10% of these individuals become symptomatic and develop colitis and liver abscess with a mortality rate of more than 40,000 persons each year. The current methods of diagnosis is the microscopic visualization of the organism in fecal specimens. However, this method requires extensive experience, is tedious, and may not be accurate if not performed within minutes of collecting the specimen. In addition, t does not distinguish nonpathogenic and pathogenic strains. This is a major drawback because nonpathogenic strains do not cause disease and persons infected with nonpathogenic strains do not require treatment with antiamebic drugs, which have a number of harsh side effects. The following project will evaluate the use of monoclonal antibody-based ELISAs designed to detect the presence of the organism in fecal specimens and to distinguish nonpathogenic from pathogenic strains. The ELISAs are based on the use of monoclonal antibodies that bind specifically to the galactose adhesin of the organism. The project will optimize the ELISA as a diagnostic test and begin to analyze fecal specimens as well as liver biopsy and serum specimens for the presence of E.histolytica antigen. Results will be correlated with microscopy results and with zymodeme analysis, which is expensive and tedious and is the only current means of distinguishing nonpathogenic from pathogenic strains. The ELISA tests, which will be scaled up for commercial application, should be useful as diagnostic aids and will make the diagnosis more efficient and cost-effective.